Method of driving touch panel, capacitance-type touch panel, and display apparatus with touch detection function

ABSTRACT

A capacitance-type touch panel, allowing disturbance noise and touch detection time to be reduced and having a simple configuration, is provided. The capacitance-type touch panel including: a plurality of drive electrodes each having a strip shape; a drive control circuit performing control such that a drive signal for touch detection is selectively applied to the drive electrodes; a plurality of touch detection electrodes arranged to intersect with the drive electrodes in such a manner that capacitance is formed in each intersecting part, and each outputting a detection signal in synchronization with the drive signal; and a detection circuit detecting an external proximity object based on the detection signal. The drive control circuit controls application of the drive signal in such a manner that the detection signal is a polarity-alternating signal including a positive-negative asymmetrical signal component which is due to presence of the external proximity object.

CROSS REFERENCES TO RELATED APPLICATIONS

The subject matter of application Ser. No. 12/794,289 is incorporatedherein by reference. The present application is a Continuation of U.S.Ser. No. 12/794,289, filed Jun. 4, 2010, which claims priority toJapanese Patent Application No. JP2009-154207 filed in the JapanesePatent Office on Jun. 29, 2009, the entire content of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a touch panel that may be inputted withinformation by contact or approach of a user with a finger or the like,and particularly relates to a method of driving a touch panel detectingtouch based on change in capacitance, and a touch panel and a displayapparatus with a touch detection function using the method each.

2. Description of Related Art

A display device is recently noticed, in which a contact detector,so-called touch panel, is mounted on a display device such as liquidcrystal display device, and various button images are displayed on thedisplay device so as to allow information input as a substitute fortypical mechanical buttons. While several types of touch panels,including an optical type and a resistance type, exist, acapacitance-type touch panel is particularly expected for a mobileterminal because of a relatively simple structure and low powerconsumption. However, in the case of the capacitance-type touch panel, ahuman body acts as an antenna receiving noise (hereinafter, calleddisturbance noise) caused by an inverter fluorescent lamp, an AMbroadcast wave, an AC power supply and the like, and the noise may betransmitted to the touch panel, causing malfunction.

The malfunction is due to a fact that a signal on presence of touch(hereinafter, called touch signal) generated by contact or approach of auser with a finger is hardly distinguished from disturbance noise. Thetouch signal is typically A/D converted (sampled) by a detection circuitwith folding noise being generated. Specifically, when a signal having afrequency component higher than a Nyquist frequency is sampled, thesignal is folded with the Nyquist frequency as a reference, andoutputted as a signal having a frequency component lower than theNyquist frequency. Therefore, when disturbance noise having a frequencycomponent higher than the Nyquist frequency is inputted to the detectioncircuit, frequency of such a noise component is equivalent to be in afrequency band equal to or lower than the Nyquist frequency. Thus, thedisturbance noise is hardly distinguished from a touch signal to benormally detected in the frequency band equal to or lower than theNyquist frequency.

Thus, for example, United States Patent Application Publication2007/0257890 proposes a method, in which when a touch signal isdetected, the touch signal being in synchronization with a signal(hereinafter, drive signal) driving a capacitance-type touch panel, aplurality of drive signals having different frequencies are used toselect a condition, at which a touch signal is hardly affected bydisturbance noise, for detection of the touch signal. In the method, adetection circuit uses the drive signals having different frequencies tosample a touch signal at a plurality of sampling frequenciescorresponding to the drive signals, which inevitably leads to change inNyquist frequency. That is, a folding reference is changed. Therefore,when disturbance noise having a high frequency component compared withthe Nyquist frequency is inputted to the detection circuit, a frequencyof a noise component equivalent to the disturbance noise, the noisecomponent appearing in a frequency band not higher than the Nyquistfrequency, is changed depending on the Nyquist frequency. In contrast, afrequency of a touch signal component is not changed even if the Nyquistfrequency is changed. Therefore, the Nyquist frequency is selected suchthat the equivalent noise component may be distinguished from the touchsignal component, so that the disturbance noise may be distinguishedfrom the touch signal.

SUMMARY OF THE INVENTION

However, in the drive method of the capacitance-type touch panel and thedetection method thereof disclosed in the above-mentioned United Statespatent application Publication, since a frequency of a drive signalneeds to be sequentially changed to select a condition at which a touchsignal is hardly affected by disturbance noise, much time may be takenfor selecting the condition. That is, detection time may be increased.Furthermore, preparation of drive signals having a plurality offrequencies is necessary, and switching timing of the signals needs tobe determined, so that a circuit configuration may be complicated andlarge.

As another method of removing the disturbance noise, a generally-knownnoise filter is considered to be used. For example, a low-pass filterhaving a cutoff frequency lower than the relevant Nyquist frequency isinserted before A/D conversion, thereby folding noise may be removed.Thus, the disturbance noise may be removed, and a detection circuit maybe simplified after A/D conversion. However, a touch signal insynchronization with a drive signal outputted from a touch panel is apositive-negative symmetrical polarity-alternating signal and thereforemay not pass through the low-pass filter. Specifically, the low-passfilter removes not only the disturbance noise but also the touch signal.

It is desirable to provide a method of driving a touch panel, in whichpresence of touch may be securely detected while influence of thedisturbance noise and touch detection time are reduced despite using arelatively simple circuit configuration, and provide a touch panel and adisplay apparatus with a touch detection function using the drive methodeach.

A capacitance-type touch panel according to an embodiment of theinvention includes a drive control circuit, a plurality of driveelectrodes, a plurality of touch detection electrodes, and a detectioncircuit. The drive control circuit performs control such that a drivesignal for touch detection is selectively applied to the driveelectrodes. The drive electrodes each have a strip shape, andselectively applied with a drive signal. The touch detection electrodesare arranged to intersect with the drive electrodes in such a mannerthat capacitance is formed in each intersecting part, and each outputs adetection signal in synchronization with the drive signal. The detectioncircuit detects an external proximity object based on the detectionsignal. In particular, the drive control circuit controls application ofthe drive signal in such a manner that the detection signal comes to bea polarity-alternating signal including a positive-negative asymmetricalsignal component which is due to presence of the external proximityobject.

A display apparatus with a touch detection function according to anembodiment of the invention has the capacitance-type touch panelaccording to the embodiment of the invention. In this case, the displayapparatus may be configured such that the drive signal for touchdetection also serves as part of a display drive signal.

A method of driving a touch panel according to an embodiment of theinvention includes the steps of: selectively applying a drive signal fortouch detection to a plurality of drive electrodes each having a stripshape; allowing each of a plurality of touch detection electrodes tooutput a detection signal in synchronization with the drive signal whena external proximity object exists, the touch detection electrodes beingarranged to intersect with the drive electrodes in such a manner thatcapacitance is formed in each intersecting part, and the detectionsignal being a polarity-alternating signal including a positive-negativeasymmetrical signal component which is due to presence of a externalproximity object; and detecting the external proximity object based onthe detection signal.

In the method of driving a touch panel, the capacitance-type touchpanel, and the display device with a touch detection function accordingto the embodiment of the invention, when a drive signal is selectivelyapplied to a plurality of drive electrodes, a polarity-alternatingsignal, as a detection signal, in correspondence to capacitance betweeneach drive electrode and each touch detection electrode is outputtedfrom the touch detection electrode. At that time, when an externalproximity object such as a finger exists, capacitance between a driveelectrode and a touch detection electrode in a part corresponding to theobject is changed, and change in waveform corresponding to such changein capacitance (touch component) appears in the detection signal. Thetouch component is a positive-negative asymmetrical signal component dueto presence of the external proximity object. Such positive-negativeasymmetry results in a phenomenon that even if signal processing of thedetection signal is performed via an analog filter for noise removal,the touch component is not removed from the detection signal.

The touch component appearing in the detection signal may havepositive-negative asymmetry by several methods.

In a first method, a signal, which has a periodical waveform including aperiod of a first voltage, and a period of a second voltage differentfrom the first voltage, is used as a drive signal, a first group ofdrive electrodes and a second group of drive electrodes are selectedfrom a plurality of drive electrodes, and the first voltage and thesecond voltage of the drive signal are applied to the selected driveelectrodes of the first and second groups, respectively. The driveelectrodes are selected in such a manner that, a total width of driveelectrodes, belonging to the first group of drive electrode, within abase width corresponding to size of an external proximity object isdifferent from a total width of drive electrodes, belonging to thesecond group of drive electrodes, within the base width, at any positionin a region where the drive electrodes are arranged. Thus, magnitude ofcapacitance between the drive electrode and the touch detectionelectrode is different between an application period of the firstvoltage of the drive signal and an application period of the secondvoltage thereof, as a result, the touch component in thepolarity-alternating detection signal becomes positive-negativeasymmetrical.

In the first method, furthermore, it is preferable that all the secondgroup of drive electrodes are discretely divided into a plurality of subgroups, and a drive signal is applied to drive electrodes of each subgroup. In this case, furthermore, it is preferable that total width ofall the first group of drive electrodes is equal to total width of allthe second group of drive electrodes. For example, in the case that anin-cell type touch panel integrated with a display device is configured,touch detection operation is hardly affected by internal noiseassociated with writing to a display element.

In a second method, a signal, which has a periodical waveform includinga period of a first voltage, and a period of a second voltage differentfrom a first voltage, is used as a drive signal, a group of driveelectrodes configuring a single strip region are selected from aplurality of drive electrodes, and a first voltage of the drive signalis applied to the group of drive electrodes and a second voltage is notapplied to any drive electrode. In the method, a touch component appearsin a detection signal only in an application period of the first voltageof the drive signal, and does not appear in an application period of thesecond voltage. As a result, a touch component in thepolarity-alternating detection signal becomes positive-negativeasymmetrical.

According to the method of driving a touch panel, the capacitance-typetouch panel, and the display device with a touch detection function ofthe embodiment of the invention, when an external proximity objectexists, a touch component included in a detection signal from a touchdetection electrode has positive-negative asymmetry, therefore even ifsignal processing of a detection signal is performed via an analogfilter for noise removal, the touch component is not removed from thedetection signal. Therefore, the touch signal may be securely detectedwhile removing disturbance noise. Moreover, since processing ofsequentially changing frequency of a drive signal to select a detectioncondition is unnecessary unlike in the past, reduction in size of adetection circuit and decrease in detection time may be achieved.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams for illustrating a principle of a touchdetection method of a display apparatus with a touch detection functionaccording to an embodiment of the invention, showing a noncontact ornon-approach state of a finger.

FIGS. 2A and 2B are diagrams for illustrating the principle of the touchdetection method of the display apparatus with a touch detectionfunction according to the embodiment of the invention, showing a contactor approach state of a finger.

FIG. 3 is a diagram for illustrating the principle of the touchdetection method of the display apparatus with a touch detectionfunction according to the embodiment of the invention, showing anexample of each waveform of a drive signal and a detection signal.

FIG. 4 is a block diagram showing a configuration example of a displayapparatus with a touch detection function according to a firstembodiment of the invention.

FIG. 5 is a section diagram showing a schematic section structure of adisplay device with a touch detection function shown in FIG. 4.

FIG. 6 is a circuit diagram showing pixel arrangement of the liquidcrystal display device shown in FIG. 4.

FIG. 7 is a perspective diagram showing a configuration example of driveelectrodes and touch detection electrodes of the touch sensor shown inFIG. 4.

FIGS. 8A and 8B are schematic diagrams showing an example of a selectionstate of a drive electrode according to the display device with a touchdetection function shown in FIG. 4.

FIG. 9 is a timing chart for illustrating operation of the displayapparatus with a touch detection function shown in FIG. 4.

FIGS. 10A and 10B are charts showing an example of waveforms in a longtime scale in the display apparatus with a touch detection functionshown in FIG. 4.

FIG. 11 is a chart showing an example of timing in the case withinternal noise when touch operation is not performed in the displayapparatus with a touch detection function shown in FIG. 4.

FIG. 12 is a chart showing an example of timing in the case withinternal noise when touch operation is performed in the displayapparatus with a touch detection function shown in FIG. 4.

FIGS. 13A and 13B are schematic diagrams showing an example of aselection state of a drive electrode according to a modification of thefirst embodiment.

FIGS. 14A and 14B are schematic diagrams showing an example of aselection state of a drive electrode according to another modificationof the first embodiment.

FIG. 15 is a block diagram showing a configuration example of a displayapparatus with a touch detection function according to a secondembodiment of the invention.

FIGS. 16A and 16B are schematic diagrams showing an example of aselection state of a drive electrode according to a display device witha touch detection function shown in FIG. 15.

FIG. 17 is a chart showing an example of timing in the display apparatuswith a touch detection function shown in FIG. 15.

FIG. 18 is a chart showing an example of timing in the case withinternal noise when touch operation is not performed in the displayapparatus with a touch detection function shown in FIG. 15.

FIG. 19 is a view showing a general configuration of an applicationexample 1 among display apparatuses with a touch detection function eachusing the embodiments.

FIGS. 20A and 20B show a general configuration of an application example2, where FIG. 20A is a perspective view showing appearance as viewedfrom a front side, and FIG. 20B is a perspective view showing appearanceas viewed from a back side.

FIG. 21 is a perspective view showing a general configuration of anapplication example 3.

FIG. 22 is a perspective view showing a general configuration of anapplication example 4.

FIGS. 23A to 23G show a general configuration of an application example5, where FIG. 23A is a front view of the example in an opened state,FIG. 23B is a side view thereof, FIG. 23C is a front view of the examplein a closed state, FIG. 23D is a left-side view thereof, FIG. 23E is aright-side view thereof, FIG. 23F is a top view thereof, and FIG. 23F isa bottom view thereof.

FIG. 24 is a section diagram showing a schematic section structure of adisplay device with a touch detection function according to amodification of the first and second embodiments.

FIG. 25 is a block diagram showing a configuration example of a touchpanel according to a modification of the first embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be described indetail with reference to drawings. Description is made in the followingsequence.

1. Principle of capacitance-type touch detection

2. First Embodiment

3. Second Embodiment

4. Application examples

5. Other modifications

1. Principle of Capacitance-Type Touch Detection

First, a principle of a touch detection method of each of a touch paneland a display apparatus with a touch detection function according toembodiments of the invention is described with reference to FIGS. 1A and1B to FIG. 3. The touch detection method is embodied as acapacitance-type touch sensor, in which a pair of electrodes (a driveelectrode E1 and a detection electrode E2) oppositely disposed with adielectric D in between are used to configure a capacitative element,for example, as shown in FIG. 1A. Such a structure is represented as anequivalent circuit shown in FIG. 1B. The drive electrode E1, thedetection electrode E2, and the dielectric D collectively configure acapacitative element C1. One end of the capacitative element C1 isconnected to an AC signal source (drive signal source) S, and the otherend P thereof is grounded via a resistor R and connected to a voltagedetector (detection circuit) DET. When an AC square wave Sg (part B inFIG. 3) having a predetermined frequency (for example, about several tomore than ten kHz) is applied from the AC signal source S to the driveelectrode E1 (one end of the capacitative element C1), an outputwaveform (detection signal Vdet) as shown in part A in FIG. 3 appears inthe detection electrode E2 (the other end P of the capacitative elementC1). The AC square wave Sg corresponds to a drive signal Vcom describedlater.

In a noncontact (or non-approach) state of a finger, a current I0corresponding to a capacitance value of the capacitative element C1flows along with charge and discharge of the capacitative element C1 asshown in FIGS. 1A and 1B. In this case, a potential waveform at theother end P of the capacitative element C1 is, for example, similar to awaveform V0 in part A in FIG. 3, which is detected by the voltagedetector DET.

In contrast, in a contact (or approach) state of a finger, acapacitative element C2 formed by the finger is added in series to thecapacitative element C1 as shown in FIGS. 2A and 2B. In this state, acurrent I1 and I2 flows with charge and discharge of the capacitativeelement C1 or C2, respectively. In this case, a potential waveform atthe other end P of the capacitative element C1 is, for example, similarto a waveform V1 in part A in FIG. 3, which is detected by the voltagedetector DET. At that time, a potential of a point P becomes a dividedpotential determined by values of the currents I1 and I2 flowing throughthe respective capacitance elements C1 and C2. Therefore, the waveformV1 has a small value compared with a value of the waveform V0 in thenoncontact state. The voltage detector DET compares a detected voltageto a predetermined threshold voltage Vth. When the detected voltage isequal to or higher than the threshold voltage, the voltage detectordetermines the state as a noncontact state, and when the detectedvoltage is lower than the threshold voltage, the voltage detectordetermines the state as a contact state. In this way, touch detection isenabled.

2. First Embodiment Configuration Example General Configuration Example

FIG. 4 shows a configuration example of a display apparatus with a touchdetection function according to a first embodiment of the invention.Since a method of driving a touch panel according to an embodiment ofthe invention is embodied by the embodiment, the method is describedtogether. The display apparatus is a so-called in-cell type apparatuswhere liquid crystal display elements are used as display elements, andbesides, a liquid crystal display device configured of the liquidcrystal display elements is integrated with a capacitance-type touchsensor.

The display apparatus with a touch detection function 40 includes a Vcomgenerator 41, a drive control circuit 42, a drive electrode driver 43, adisplay device with a touch detection function 44, a gate driver 45, asource driver 46, a multiplexer 47, a detection circuit 48, and aresistance R.

The Vcom generator 41 is a circuit generating a drive signal Vcom usedin the display device with a touch detection function 44. Here, thedrive signal Vcom is a polarity-alternating square wave as shown in partA in FIG. 9 described later, and therefore has a positive range (periodof a first voltage) and a negative range (period of a second voltage).Specifically, each liquid crystal display element of the embodiment isdriven by a so-called polarity-reversal drive method in which a polarityof an applied voltage to a liquid crystal element is reversed every onehorizontal pixel line (1H).

The drive electrode control section 42 selects and controls an electrodeof a plurality of drive electrodes of the display device 44 when thedrive signal Vcom supplied from the Vcom generator 41 is supplied to theelectrodes. At that time, the drive electrode control section 42 maycontrol a layout, number and scan-movement of drive electrodes to beapplied with the drive signal Vcom depending on polarity (positive ornegative polarity) of the drive signal Vcom. In particular, the driveelectrode control section 42 of the embodiment may perform control ofchanging a layout pattern of drive electrodes to be applied with thedrive signal Vcom between the positive and negative ranges of the drivesignal Vcom while number of drive electrodes to be applied with thedrive signal Vcom is kept to a certain number in each of the positiveand negative ranges.

The drive electrode driver 43 is a circuit supplying the drive signalVcom supplied from the Vcom generator 41 to the drive electrodes of thedisplay device with a touch detection function 44 described lateraccording to a control signal from the drive control circuit 42.

The display device with a touch detection function 44 has a touch sensor441 and a liquid crystal display device 442. The touch sensor 441outputs a detection signal Vdet having a waveform, for example, as shownin part B and part C in FIG. 9 based on the principle ofcapacitance-type touch detection. The detection signal Vdet includes asignal component due to touch operation (hereinafter, called “touchcomponent”) as will be described later.

The gate driver 45 is a circuit supplying a signal for selecting ahorizontal pixel line to be displayed to the liquid crystal displaydevice 442. The source driver 46 is a circuit supplying an image signalto the liquid crystal display device 442. The multiplexer 47 is acircuit where whenever the detection signal Vdet is sequentiallyextracted from a plurality of touch detection electrodes (describedlater) of the touch sensor 441, the circuit switches a source of suchextraction.

The detection circuit 48 detects presence of touch to the touch sensor441 based on the detection signal Vdet switched by the multiplexer 47,and furthermore obtains coordinates of a touch point on a touch panel.The detection circuit 48 includes analog LPF (Low-Pass Filter) 51, anA/D converter 52, a signal processor 53, and a coordinate extractionsection 54. The analog LPF 51 is a low-pass analog filter that removes ahigh frequency component from the detection signal Vdet, and thenoutputs such a processed signal. The analog LPF 51 is inserted to removefolding noise generated in the A/D converter 52 described later. The A/Dconverter 52 is a circuit converting an analog signal outputted from theanalog LPF 51 into a digital signal. The signal processor 53 is a logiccircuit detecting presence of touch to the touch sensor 441 based on anoutput signal from the A/D converter 52. The coordinate extractionsection 54 is a logic circuit obtaining coordinates on the touch panelat which presence of touch is detected by the signal processor 53.

These circuits are controlled by a not-shown timing controller.

Configuration Example of Display Device with a Touch Detection Function44

FIG. 5 shows an example of a relevant-part section structure of thedisplay device with a touch detection function 44. The display device 44includes a pixel substrate 2, a counter substrate 3 disposed facing thepixel substrate 2, and a liquid crystal layer 6 inserted between thepixel substrate 2 and the counter substrate 3.

The pixel substrate 2 has a TFT substrate 21 as a circuit board, and aplurality of pixel electrodes 22 arranged in a matrix pattern on the TFTsubstrate 21. TFT (Thin Film Transistor) of each pixel, and wirings suchas a source line supplying an image signal to each pixel electrode and agate line driving each TFT, which are not shown, are formed on the TFTsubstrate 21. In addition, the TFT substrate 21 may be formed includingpart or all of the circuit shown in FIG. 4.

The counter substrate 3 has a glass substrate 31, a color filter 32formed on one surface of the glass substrate 31, and a drive electrode33 formed on the color filter 32. The color filter 32 includes, forexample, color filter layers of three colors of red (R), green (G) andblue (B) being periodically arranged, where a set of RGB three-colorfilters is set in correspondence to each display pixel. The driveelectrode 33 acts as a common drive electrode of the liquid crystaldisplay device 442, and besides, shared as a drive electrode of thetouch sensor 441. The drive electrode 33 is connected to the TFTsubstrate 21 by a contact conduction pole 7. The drive signal Vcomhaving an AC square waveform is applied from the TFT substrate 21 to thedrive electrode 33 via the contact conduction pole 7. The drive signalVcom, which may be called common drive signal, defines a pixel voltageapplied to the pixel electrode 22 and a display voltage of each pixel.Furthermore, the drive signal Vcom is used even as a drive signal of thetouch sensor.

A touch detection electrode 34 as a detection electrode of the touchsensor 441 is formed on the other surface of the glass substrate 31, andfurthermore, a polarizing plate 35 is disposed on the touch detectionelectrode 34.

The liquid crystal layer 6 modulates light passing through the liquidcrystal layer 6 depending on a state of an electric field. Various modesof liquid crystal are used for the liquid crystal layer 6, the modesincluding a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode,an ECB (Electric-Field Control Birefringence) mode and the like.

An alignment film is disposed between the liquid crystal layer 6 and thepixel substrate 2, and between the liquid crystal layer 6 and thecounter substrate 3, respectively, and an incidence-side polarizingplate is disposed on a bottom side of the pixel substrate 2, each ofwhich is omitted to be shown here.

FIG. 6 shows a configuration example of a pixel structure of the liquidcrystal display device 442. In the liquid crystal display device 442, aplurality of display pixels 20, each display pixel having a TFT elementTr and a liquid crystal element LC, are arranged in a matrix pattern.

Each display pixel 20 is connected with a source line 25, a gate line26, and the drive electrode 33 (here, for example, n electrodes 331 to33 n (n: an integer of 2 or more)). The source line 25 is a signal linefor supplying an image signal to each display pixel 20, and connected tothe source driver 46. The gate line 26 is a signal line for supplying asignal selecting a display pixel 20 for display, and connected to thegate driver 45. In this example, each gate line 26 is connected to alldisplay pixels 20 being horizontally arranged. That is, the liquidcrystal display device 442 displays an image for each horizontal pixelline according to a control signal of each gate line 26. The driveelectrode 33 applies a drive signal for driving the liquid crystal, andconnected to the drive electrode driver 43. In the example, each driveelectrode is connected to all display pixels 20 being horizontallyarranged. That is, the liquid crystal display device 442 is driven foreach horizontal pixel line according to a drive signal of each driveelectrode.

FIG. 7 perspectively shows a configuration example of the driveelectrode 33 (331 to 33 n) and the touch detection electrode 34 of thecounter substrate 3 in the touch sensor 441. The drive electrode 33 isdivided into a plurality of stripe electrode patterns extending in ahorizontal direction in the figure. Each electrode pattern issequentially supplied with the drive signal Vcom (part A in FIG. 9) bythe drive electrode driver 43, so that line-sequential scan drive istime-divisionally performed as will be described later. In contrast, thetouch detection electrode 34 includes a plurality of stripe electrodepatterns extending in a direction orthogonal to the extending directionof the electrode patterns of the drive electrode 33. Each of theelectrode patterns of the touch detection electrode 34 outputs adetection signal Vdet (part B and part C in FIG. 9), and the detectionsignal is inputted to the detection circuit 48 via the multiplexer 47.

The electrode patterns intersecting with each other formed by the driveelectrode 33 and the touch detection electrode 34 form capacitance ateach of the intersecting parts. The drive electrode 33 corresponds tothe drive electrode E1 shown in FIGS. 1A and 1B and FIGS. 2A and 2B forillustrating the principle of capacitance-type touch detection. On theother hand, the touch detection electrode 34 corresponds to thedetection electrode E2 shown in FIGS. 1A and 1B and FIGS. 2A and 2B.Thus, the touch sensor may detect touch in accordance with the principleof capacitance-type touch detection. Furthermore, the touch sensor isconfigured in a matrix pattern by the electrode patterns intersectingwith each other. Therefore, a position where contact or approach of anobject occurs may be detected.

Operation and Effects

General Basic-Operation

First, general operation of the display apparatus with a touch detectionfunction 40 of the embodiment is described.

The Vcom generator 41 generates a drive signal Vcom, and supplies thesignal to the drive electrode driver 43. The drive electrode driver 43supplies the drive signal Vcom to the drive electrodes 331 to 33 n ofthe display device with a touch detection function 44 while sequentiallyswitching the drive electrodes according to a control signal from thedrive control circuit 42. The drive control circuit 42 performs controlsuch that a drive electrode supplying the drive signal Vcom is selectedfrom the drive electrodes 331 to 33 n in accordance with a voltage levelof the drive signal Vcom. Such selection is separately performed(performed as separate selection process) for the touch sensor 441 andfor the liquid crystal display device 442.

Each touch detection electrode 34 of the touch sensor 441 outputs adetection signal Vdet with a waveform having rising and falling insynchronization with voltage change timing of the drive signal Vcombased on the principle of capacitance-type touch detection. Themultiplexer 47 successively extracts the detection signal Vdet outputtedfrom each touch detection electrode 34 of the touch sensor 441 bysequentially switching an extraction source, and sends the signal to thedetection circuit 48. In the detection circuit 48, the analog LPF 51removes a high-frequency component from the detection signal Vdet, andoutputs the signal as a detection signal Vdet2. The A/D converter 52converts the detection signal Vdet2 from the analog LPF 51 into adigital signal. The signal processor 53 determines presence of touch tothe touch sensor 441 by logical operation based on an output signal fromthe A/D converter 52. The coordinate extraction section 54 detectscoordinates of a touch point on the touch sensor based on a touchdetection result by the signal processor 53. In this way, when a usertouches the touch panel, a position of the relevant touch is detected.

The source driver 46 supplies an image signal to the liquid crystaldisplay device 442. The gate driver 45 supplies a selection signal (gatesignal) for selecting a horizontal pixel line to be displayed to theliquid crystal display device 442. In the liquid crystal display device442, the whole screen is line-sequentially scanned for each horizontalpixel line based on the image signal, the gate signal and a drivesignal, so that an image is displayed on the screen. More particularly,in FIG. 6, a pixel signal is supplied via a source line 25 and thenapplied to a pixel electrode 22 of the liquid crystal element LC via aTFT element Tr of a line-sequentially selected display pixel 20 by thegate line 26, and the polarity-alternating drive signal Vcom (part A inFIG. 9) is applied to the common electrode (drive electrode 33). Thus,pixel data are written into the liquid crystal element LC for imagedisplay.

Next, features of the embodiment are described in detail.

Operation Example of Drive Control Circuit 42

The drive control circuit 42 selects a drive electrode, to which thedrive signal Vcom is applied by the drive electrode driver 43, from thedrive electrodes 33 of the display device with a touch detectionfunction 44. Such selection is separately performed for the touch sensor441 and for the liquid crystal display device 442.

FIGS. 8A and 8B show an operation example of a drive electrode appliedwith the drive signal Vcom, where FIG. 8A shows an operation examplewhen a voltage of the drive signal Vcom has a high level, and FIG. 8Bshows an operation example when a voltage of the drive signal Vcom has alow level, as an operation example immediately after operation of FIG.8A.

In FIGS. 8A and 8B, a drive electrode applied with a drive signal Vcomused for driving the touch sensor 441 is divided into a detection driveline group L1P (first group) applied with a first voltage in a positiverange, and a detection drive line group IAN (second group) applied witha second voltage in a negative range. The detection drive line group UPincludes continuously adjacent, a series of drive electrodes,collectively forming a single, thick strip drive electrode. In contrast,the detection drive line group L1N includes a plurality of driveelectrodes dispersed one by one over the whole panel surface. Thus,wherever a proximity object such as a finger is on the touch sensor 441,number of drive electrodes in a region where the proximity objectoverlaps with the detection drive line group L1P is different fromnumber of drive electrodes in a region where the proximity objectoverlaps with the detection drive line group L1N. In other words, totalwidth W1 of the first group of the drive electrodes in a base width Wcorresponding to size of the proximity object is different from totalwidth W2 of the second group of the drive electrodes in the base widthW, and W1>W2 is given in the shown example. On the other hand, a driveelectrode applied with the drive signal Vcom used for driving the liquidcrystal display device 442 includes a single display drive line L2 ineach of the positive and negative ranges. In the embodiment, totalnumber of the drive electrodes is the same between the first and secondgroups.

As shown in FIGS. 8A and 8B, the display drive line L2 is sequentiallyscan-moved over the whole surface of the liquid crystal display device442 in synchronization with polarity alternation of the drive signalVcom. Specifically, the display drive line L2 is alternately appliedwith a positive voltage (first voltage) and a negative voltage (secondvoltage) for each movement by one horizontal pixel line. Furthermore,the gate driver 45 sequentially scans the same horizontal pixel line insynchronization with the display drive line L2. Thus, an image signal issupplied from the source line 25 to a selected, horizontal pixel line sothat data are written to each pixel of the horizontal image line. Suchoperation is line-sequentially repeated, thereby an image is displayedon the liquid crystal display device 442.

In drive of the touch sensor 441, as shown in FIGS. 8A and 8B, number ofdrive electrodes applied with the drive signal Vcom or a layout patternthereof is different depending on polarity ranges of the drive signalVcom. Specifically, in the positive range of the drive signal Vcom, asshown in FIG. 8A, the detection drive line group L1P, which configures asingle, thick strip drive electrode, is selected, and applied with thepositive voltage (first voltage). The single strip drive electrode issequentially scan-moved by one horizontal pixel line in synchronizationwith the display drive line L2. Such scan is performed to detect aposition at which a finger contacts or approaches the touch sensor 441.In contrast, in the negative range of the drive signal Vcom, as shown inFIG. 8B, the detection drive line group L1N including dispersed driveelectrodes is selected, and the drive electrodes are collectivelyapplied with the negative voltage (second voltage).

Operation Example of Touch Sensor 441

Next, operation example of the touch sensor 441 is described in moredetail.

FIG. 9A shows an example of timing of the display apparatus with a touchdetection function 40, where part A in FIG. 9 shows a waveform of thedrive signal Vcom, part B in FIG. 9 shows a waveform of the detectionsignal Vdet when touch operation is not performed, and part C in FIG. 9shows a waveform of the detection signal Vdet when touch operation isperformed. Part B and part C in FIG. 9 show an example of a detectionwaveform for one of the touch detection electrodes 34. In a so-calledin-cell type apparatus, in which the touch sensor is integrated with thedisplay device as in the embodiment, internal noise generated in theliquid crystal display device 442 may appear in the detection signalVdet as output of the touch sensor 441 as described later. Thus,description is separately made for the case with internal noise and forthe case without internal noise.

(1) Operation in the Case without Internal Noise

As shown in part B in FIG. 9, a waveform of the detection signal Vdet inthe case that touch operation is not performed is a positive-negativesymmetrical signal waveform in synchronization with polarity alternationof the drive signal Vcom. This is because total number of driveelectrodes to be a drive object is not different between the positiverange (detection drive line group L1P) of the drive signal Vcom and thenegative range (detection drive line group L1N) thereof, as shown inFIGS. 8A and 8B. That is, when a particular touch detection electrode isnoticed, capacitance of an intersecting part between the touch detectionelectrode and the detection drive line group LIP is equal to capacitanceof an intersecting part between the same touch detection electrode andthe detection drive line group L1N, and therefore an equivalent circuitof FIG. 1B is also not changed by polarity-alternating operation of thedrive signal Vcom.

In this way, in the state where touch operation is not performed, atime-average level of the detection signal Vdet is approximatelycorresponding to a center voltage of the waveform of the detectionsignal Vdet due to the positive-negative symmetry of the detectionsignal Vdet.

In contrast, as shown in part C in FIG. 9, a waveform of the detectionsignal Vdet in the case that touch operation is performed is apositive-negative asymmetrical signal waveform in synchronization withpolarity alternation of the drive signal Vcom. This is because when afinger contacts or approaches the touch sensor 441, overlapping areabetween the finger and the detection drive line group LIP is differentfrom overlapping area between the finger and the detection drive linegroup L1N as shown in FIGS. 8A and 8B. That is, in the positive range ofthe drive signal Vcom, such overlapping area is large, so that change incapacitance due to presence of touch operation is large, and therefore adegree of decrease in amplitude of the detection signal Vdet isincreased compared with the case that touch operation is not performed.In contrast, in the negative range of the drive signal Vcom, suchoverlapping area is small, so that change in capacitance due to presenceof touch is small, and therefore a degree of decrease in amplitude ofthe detection signal Vdet is reduced compared with the case that touchoperation is not performed.

In the state where touch operation is performed, a time-average level ofthe detection signal Vdet is shifted to a low voltage side (negativeside) with respect to the center voltage of the waveform of thedetection signal Vdet due to the positive-negative asymmetry of thedetection signal Vdet. Frequency of occurrence of a section shifted tothe low voltage side is sufficiently low, and the frequency directlypasses through the analog LPF in a later stage. Therefore, only such alow-frequency component may be extracted, and presence of touchoperation may be thus detected.

FIGS. 10A and 10B show a waveform example in a longer time scale, whereFIG. 1 OA shows a waveform of the detection signal Vdet, and FIG. 10Bshows a waveform of the detection signal Vdet2 outputted from the analogLPF 51. As known from FIG. 10A, in a period of touch operation, an upperenvelope level of the waveform of the detection signal Vdet is morereduced due to the positive-negative asymmetry of the detection signalVdet. When this waveform is inputted to the analog LPF 51, ahigh-frequency component is removed from the waveform, and a touchdetection signal corresponding to presence of touch appears in output ofthe LPF 51 as shown in FIG. 10B.

The reason why the detection signal Vdet2 as in FIG. 10B appears inoutput of the analog LPF 51 is because positive-negative symmetry of thedetection signal Vdet is changed between the case that touch operationis performed and the case that touch operation is not performed asillustrated in part B and part C in FIG. 9. Therefore, even if amplitudeof the detection signal Vdet is changed between the case that touchoperation is performed and the case that touch operation is notperformed, a signal as shown in FIG. 10B does not appear in output ofthe analog LPF 51 as long as the waveform of the detection signal Vdetis positive-negative symmetric. This means that internal noise that maybe in positive-negative symmetrical is also removed by the analog LPF 51as described later.

The display apparatus with a touch detection function 40 converts thewaveform of the detection signal Vdet2 shown in FIG. 10B into a digitalsignal by the A/D converter 52. A cutoff frequency of the analog LPF 51is desirably set low to the utmost as long as a low-frequency signalcomponent (FIG. 10B) generated by contact or approach of a user with afinger may pass through the LPF. If the cutoff frequency is set lowcompared with a Nyquist frequency calculated from a sampling frequencyof the A/D converter 52, folding noise is removed. Thus, the displayapparatus 40 may extremely reduce influence of disturbance noise havinga frequency component equal to or higher than the Nyquist frequency.

(2) Operation in the Case with Internal Noise

Next, influence of internal noise generated by the liquid crystaldisplay device 442 on the touch sensor 441 is described.

As above, when a gate signal is applied to a gate line 26 of aparticular horizontal pixel line of the liquid crystal display device442, a pixel electrode 22 of a liquid crystal display element LC on thehorizontal pixel line is supplied with a pixel signal applied from thesource line 25, and a common electrode (drive electrode 33) is suppliedwith the drive signal Vcom. Thus, information of the pixel on thehorizontal pixel line is displayed. In this writing, a signal on thesource line 25 may be transmitted to the drive electrode 33, andfurthermore, appears as internal noise in the detection signal Vdet asoutput of the touch sensor 441. In particular, the internal noise issignificantly increased in the case that all pixel signals on therelevant horizontal pixel line (namely, image signals transmittedthrough all source lines 25 at the relevant writing timing) have largevoltage amplitude (specifically, in the case that white or blackinformation is written into all pixels on the relevant horizontal pixelline).

FIG. 11 shows an example of waveforms in the case that touch operationis not performed when internal noise exists, where part A in FIG. 11shows a waveform of the drive signal Vcom, part B in FIG. 11 shows awaveform of the detection signal Vdet in writing of white information,and part C in FIG. 11 shows a waveform of the detection signal Vdet inwriting of black information. Here, Δta indicates time of writing noinformation into a pixel, and Δtb indicates time of writing informationinto a pixel.

As shown in part B and part C in FIG. 11, when a pixel is written with asignal, internal noise due to the written pixel signal appears in thedetection signal Vdet. At that time, magnitude of the internal noisedepends on magnitude of the written pixel signal (display luminance ordisplay color). However, a waveform of the detection signal Vdet is apositive-negative symmetrical waveform in synchronization with polarityalternation of the drive signal Vcom. This is because of the same reasonas in operation of the touch sensor 441 in the case without the internalnoise as shown in part B in FIG. 9. That is, this is because totalnumber of drive electrodes applied with the drive signal Vcom is notdifferent between the positive range and the negative range of the drivesignal Vcom.

In this way, in the state where touch operation is not performed, atime-average level of the detection signal Vdet is approximatelycorresponding to a center voltage of the waveform of the detectionsignal Vdet due to the positive-negative symmetry of the detectionsignal Vdet.

FIG. 12 shows an example of waveforms in the case that touch operationis performed when internal noise exists, where part A in FIG. 12 shows awaveform of the drive signal Vcom, part B in FIG. 12 shows a waveform ofthe detection signal Vdet in writing of white information, and part C inFIG. 12 shows a waveform of the detection signal Vdet in writing ofblack information. Here, Δta and Δtb have the same meaning as in thecase of FIG. 11A, respectively.

As shown in part B and part C in FIG. 12, a waveform of the detectionsignal Vdet in the case that touch operation is performed is apositive-negative asymmetrical waveform in synchronization with polarityalternation of the drive signal Vcom. This is because of the same reasonas in operation of the touch sensor 441 in the case without internalnoise as shown in part C in FIG. 9. That is, in the positive range ofthe drive signal Vcom, the relevant overlapping area is large, so thatchange in capacitance due to presence of touch operation is large, andtherefore a degree of decrease in amplitude of the detection signal Vdetis increased compared with the case that touch operation is notperformed. In contrast, in the negative range of the drive signal Vcom,the relevant overlapping area is small, so that change in capacitancedue to presence of touch operation is small, and therefore a degree ofdecrease in amplitude of the detection signal Vdet is reduced comparedwith the case that touch operation is not performed.

In the touch operation state, a time-average level of the detectionsignal Vdet is shifted to a low voltage side (negative side) withrespect to the center voltage of the waveform of the detection signalVdet due to the positive-negative asymmetry of the detection signalVdet. Frequency of occurrence of a section shifted to the low voltageside is sufficiently low, and the frequency directly passes through theanalog LPF in a later stage. Therefore, only such a low-frequencycomponent may be extracted, and presence of touch operation may be thusdetected.

Advantage

As above, in the embodiment, since the drive control circuit 42 selectsthe drive electrodes to be added with the drive signal Vcom in adifferent way (with number or a position being changed) in accordancewith a voltage level (polarity) of the drive signal Vcom as shown inFIGS. 8A and 8B, the detection signal Vdet from the touch sensor 441includes a positive-negative symmetrical signal component due totransition of a voltage level of a drive signal, and a positive-negativeasymmetrical signal component (touch component) due to touch operation.Therefore, even if an analog LPF is provided in a stage after the touchsensor, the touch component is not cancelled, and a touch detectionsignal in correspondence to presence of touch may be extracted.

Furthermore, in the embodiment, number of drive voltages added with thedrive signal Vcom does not depend on a voltage level of the drive signalVcom (in each of the positive and negative ranges), and is the same atany time, therefore influence of internal noise associated with displayoperation may be avoided.

Moreover, since frequency of a drive signal need not be sequentiallyswitched for selection of a detection condition unlike in the past,detection time may be reduced, and besides, a circuit is notcomplicated, reduction in size of an apparatus may be achieved.

Furthermore, a cutoff frequency of the analog LPF is set low comparedwith the Nyquist frequency, thereby a disturbance noise component havinga frequency higher than the Nyquist frequency may be reduced, andbesides, a frequency band of a signal is limited to a low band. Thus,the A/D converter and the signal processor are simplified, andconsequently circuit size may be further reduced.

Modification of First Embodiment

Modification 1-1

In the embodiment, when a voltage of the drive signal Vcom is positive(high level), the detection drive line group L1P is selected as in FIG.8A, and when the voltage is negative (low level), the detection driveline group L1N is selected as in FIG. 8B. However, opposite setting maybe used. Specifically, it may be designed that when a voltage of thedrive signal Vcom is negative (low level), a detection drive line groupis selected as in FIG. 8A, and when the voltage is positive (highlevel), a detection drive line group is selected as in FIG. 8B.

Modification 1-2

In the embodiment, when a voltage of the drive signal Vcom is negative,the detection drive line group L1N is configured of drive electrodesdiscretely arranged on the whole surface of the touch sensor 441.However, this is not limitative, and may be appropriately modified aslong as the following condition is satisfied: wherever a proximityobject such as a finger is on the touch sensor 441, width (number ofdrive electrodes) of a strip region overlapping with the proximityobject in the detection drive line group L1N is smaller than width(number of drive electrodes) of a strip region overlapping with theproximity object in the detection drive line group UP. For example, asshown in FIGS. 13A and 13B, when a voltage of the drive signal Vcom isnegative (low level), the drive electrodes of the detection drive linegroup L1N may be discretely located only in an upper-half region of thetouch sensor 441. Alternatively, for example, as shown in FIGS. 14A and14B, thin strip electrode portions including a plurality of driveelectrodes adjacent to one another may be dispersed over the whole panelor a partial region of the panel instead of dispersing the driveelectrodes one by one.

Modification 1-3

While the detection drive line group L1N applied with a negative voltageof the drive signal Vcom is not scan-moved in a vertical direction inthe embodiment, the group may be scan-moved in the direction.

3. Second Embodiment

Next, a display apparatus with a touch detection function according to asecond embodiment of the invention is described. Substantially the samecomponents as those of the display apparatus with a touch detectionfunction according to the first embodiment are marked with the samereference numerals or signs, and appropriately omitted to be described.

Configuration Example General Configuration Example

FIG. 15 shows a configuration example of a display apparatus with atouch detection function 140 according to the embodiment.

The display apparatus with a touch detection function 140 includes aVcom generator 41, a drive control circuit 142, a drive electrode driver43, a display device with a touch detection function 44, a gate driver45, a source driver 46, a multiplexer 47, a detection circuit 148, and aresistance R.

The drive control circuit 142 selects and controls an electrode from aplurality of drive electrodes of the display device 44 when a drivesignal Vcom is supplied from the Vcom generator 41 and then supplied tothe electrodes. At that time, the drive control circuit 142 may controla layout, number and scan-operation of drive electrodes to be appliedwith the drive signal Vcom depending on polarity (positive or negativepolarity) of the drive signal Vcom. In particular, the drive electrodecontrol section 142 of the embodiment performs control such that thedrive signal Vcom is applied to the drive electrodes only in a positiverange of the drive signal Vcom as will be described later.

The detection circuit 148 detects presence of touch to the touch sensor441 based on a detection signal Vdet switched by the multiplexer 47, andfurthermore obtains coordinates of the touch on a touch panel. Thedetection circuit 148 includes analog LPF (Low-Pass Filter) 51, an A/Dconverter 52, a signal processor 153, and a coordinate extractionsection 54. The signal processor 153 is a logic circuit detectingpresence of touch to the touch sensor 441 based on an image signal Siginputted from the outside.

These circuits are controlled by a not-shown timing controller.

Operation and Effects

Operation Example of Drive Control Circuit 142

The drive control circuit 142 selects a drive electrode, to which thedrive signal Vcom is applied by the drive electrode driver 43, from thedrive electrodes 33 of the display device 44 with a touch detectionfunction. Such selection is separately performed for the touch sensor441 and for the liquid crystal display device 442.

FIGS. 16A and 16B show an operation example of a drive electrode appliedwith the drive signal Vcom, where FIG. 16A shows an operation examplewhen a voltage of the drive signal Vcom has a high level, and FIG. 16Bshows an operation example when a voltage of the drive signal Vcom has alow level, as an operation example immediately after operation of FIG.16A.

In FIGS. 16A and 16B, a drive electrode applied with a drive signal Vcomused for driving the touch sensor 441 is only in a detection drive linegroup LIP (first group) applied with a first voltage in a positiverange. That is, any drive electrode is not used for driving the touchsensor 441. On the other hand, a drive electrode applied with a drivesignal Vcom used for driving the liquid crystal display device 442includes a single display drive line L2 in each of the positive andnegative ranges. Operation of the display drive line L2 is the same asin the first embodiment.

In drive of the touch sensor 441, as shown in FIGS. 16A and 16B, numberof drive electrodes applied with the drive signal Vcom or a layoutpattern thereof is different depending on polarity ranges of the drivesignal Vcom. Specifically, in the positive range of the drive signalVcom, as shown in FIG. 16A, the detection drive line group UP forming asingle, thick strip drive electrode is selected, and applied with apositive voltage (first voltage). The single strip drive electrode issequentially scan-moved by one horizontal pixel line in synchronizationwith the display drive line L2. Such scan is performed to detect aposition where a finger contacts or approaches the touch sensor 441. Incontrast, in the negative range of the drive signal Vcom, as shown inFIG. 16B, any drive electrode is not selected, and the touch sensor 441is not driven.

Operation Example of Touch Sensor 441

Next, operation example of the touch sensor 441 is described in moredetail.

FIG. 17 shows an example of timing in the display apparatus with a touchdetection function 140, where part A in FIG. 17 shows a waveform of thedrive signal Vcom, part B in FIG. 17 shows a waveform of the detectionsignal Vdet in the case that touch operation is not performed, and partC in FIG. 17 shows a waveform of the detection signal Vdet in the casethat touch operation is performed.

(1) Operation in the Case without Internal Noise

As shown in part B in FIG. 17, in the case that touch operation is notperformed, a waveform of the detection signal Vdet is apositive-negative asymmetrical signal waveform while being insynchronization with polarity alternation of the drive signal Vcomunlike that of part B in FIG. 9 in the first embodiment. This is becausethe detection drive line group is configured only in the positive rangeof the drive signal Vcom as shown in FIGS. 16A and 16B. That is, when aparticular touch detection electrode is noticed, since capacitance isformed in an intersecting part between the touch detection electrode andthe detection drive line group L1P only in the positive range of thedrive signal Vcom, a waveform appears in accordance with the principleof capacitance-type touch detection only in the positive range.

Furthermore, as shown in part C in FIG. 17, in the case that touchoperation is performed, a waveform of the detection signal Vdet is apositive-negative asymmetrical signal waveform while being insynchronization with polarity alternation of the drive signal Vcom. Thisis because the detection drive line group is configured only in thepositive range of the drive signal Vcom as in the case of part B in FIG.17.

In the state where touch operation is performed, a time-average level ofthe detection signal Vdet is shifted to a low voltage side (negativeside) compared with the case that touch operation is not performed.Since frequency of occurrence of a section shifted to the low voltageside is sufficiently low, and the frequency directly passes through theanalog LPF, only such a low-frequency component may be extracted, andpresence of touch operation may be thus detected.

(2) Operation in the Case with Internal Noise

Next, influence of internal noise generated by the liquid crystaldisplay device 442 on the touch sensor 441 is described.

FIG. 18 shows an example of waveforms in the case that touch operationis not performed when internal noise exists, where part A in FIG. 18shows a waveform of the drive signal Vcom, part B in FIG. 18 shows awaveform of the detection signal Vdet in writing of white information,and part C in FIG. 18 shows a waveform of the detection signal Vdet inwriting of black information.

As shown in part B and part C in FIG. 18, when a pixel is written with asignal, internal noise due to the written pixel signal appears in thedetection signal Vdet. At that time, magnitude of the internal noisedepends on magnitude of the written pixel signal (display luminance ordisplay color). Furthermore, such noise also exists only in the positiverange of the drive signal Vcom. This means that a time-average level ofthe detection signal Vdet is changed depending on a written pixelsignal. Therefore, a low-frequency component of the signal directlypasses through the analog LPF, and thus internal noise is outputteddepending on pixel signals. In this case, such internal noise may not bedistinguished from a waveform due to presence of touch operation.

Thus, in the embodiment, as shown in FIG. 15, the signal processor 153performs signal processing by using an output signal from the A/Dconverter 52 and an externally inputted image signal Sig. Specifically,amount of internal noise is calculated based on the image signal Sig,and a difference between the output signal from the A/D converter 52 andthe calculated amount of internal noise is obtained, thereby theinternal noise may be removed so that only presence of touch may bedetected. The image signal Sig may be supplied from the outside as shownin the figure, or may be supplied from the source driver 46.

Advantage

As above, in the embodiment, since the drive signal Vcom is applied tothe drive electrode only in the positive range of the drive signal Vcomas shown in FIGS. 16A and 16B, the detection signal Vdet from the touchsensor 441 includes a positive-negative asymmetrical signal component(touch component) due to touch operation. Therefore, even if an analogLPF is provided in a stage after the touch sensor, the touch componentis not cancelled, and a touch detection signal in correspondence topresence of touch may be extracted.

Furthermore, in the embodiment, since the detection circuit uses theexternally inputted image signal Sig for calculation, thepositive-negative asymmetrical signal component due to internal noisemay be removed.

Modification of Second Embodiment

Modification 2-1

While the detection drive line group L1P is selected as shown in FIG.16A only in the case that voltage of the drive signal Vcom is positive(high level) in the embodiment, opposite setting may be used.Specifically, the detection drive line group may be selected as shown inFIG. 16A only in the case that voltage of the drive signal Vcom isnegative (low level).

Modification 2-2

When a voltage of the drive signal Vcom is negative (low level), thedetection drive line is not selected in the embodiment. However, this isnot limitative, and the detection drive line group L1N may be formed insuch a case. That is, this may be appropriately modified as long as thefollowing condition is satisfied: wherever a proximity object such as afinger is on the touch sensor 441, width (number of drive electrodes) ofa strip region overlapping with the proximity object in the detectiondrive line group L1N is smaller than width (number of drive electrodes)of a strip region overlapping with the proximity object in the detectiondrive line group L1P. At that time, in each of part B and part C in FIG.17 and part B and part C in FIG. 18, a pulse appears even on a negativevoltage side, and a waveform of the pulse is positive-negativeasymmetric. Even in this case, the externally inputted image signal Sigis used for calculation, thereby the internal noise may be removed, andthe touch detection signal may be extracted.

4. Application Examples

Next, application examples of the method of driving a touch panel, thecapacitance-type touch panel, and the display apparatus with a touchdetection function, those being described in the embodiments and themodifications, are described with reference to FIG. 19 to FIG. 23G Themethod of driving a touch panel, the capacitance-type touch panel, andthe display apparatus with a touch detection function according to theembodiments and the like may be applied to electronic devices in anyfield, including a television apparatus, a digital camera, a notebookpersonal computer, a mobile terminal such as mobile phone, and a videocamera. In other words, the display apparatus according to each of theembodiments and the like may be applied to electronic devices in anyfield, which displays an externally inputted video signal or internallygenerated video signal as an image or a picture.

Application Example 1

FIG. 19 shows appearance of a television apparatus using the displayapparatus with a touch detection function according to each of theembodiments and the like. The television apparatus has, for example, afront panel 511 and a video display screen 510 including filter glass512, and the video display screen 510 is configured of the displayapparatus with a touch detection function according to each of theembodiments and the like.

Application Example 2

FIGS. 20A and 20B show appearance of a digital camera using the displayapparatus with a touch detection function according to each of theembodiments and the like. The digital camera has, for example, a lightemitting section for flash 521, a display 522, a menu switch 523 and ashutter button 524, and the display 522 is configured of the displayapparatus with a touch detection function according to each of theembodiments and the like.

Application Example 3

FIG. 21 shows appearance of a notebook personal computer using thedisplay apparatus with a touch detection function according to each ofthe embodiments and the like. The notebook personal computer has, forexample, a body 531, a keyboard 523 for input operation of letters andthe like, and a display 533 for displaying an image, and the display 533is configured of the display apparatus with a touch detection functionaccording to each of the embodiments and the like.

Application Example 4

FIG. 22 shows appearance of a video camera using the display apparatuswith a touch detection function according to each of the embodiments andthe like. The video camera has, for example, a body 541, a lens 542 forshooting an object provided on front side-face of the body 541, and astart/stop switch 543 used in shooting, and a display 544. The display544 is configured of the display apparatus with a touch detectionfunction according to each of the embodiments and the like.

Application Example 5

FIGS. 23A to 23G show appearance of a mobile phone using the displayapparatus with a touch detection function according to each of theembodiments and the like. For example, the mobile phone is formed byconnecting an upper housing 710 to a lower housing 720 by a hinge 730,and has a display 740, sub display 750, a picture light 760, and acamera 770. The display 740 or the sub display 750 is configured of thedisplay apparatus with a touch detection function according to each ofthe embodiments and the like.

5. Other Modifications

While the invention has been described with several embodiments andmodifications thereof hereinbefore, the invention is not limited to theembodiments and the like, and may be variously modified or altered.

Modification 3-1

For example, while when voltage of the drive signal Vcom is positive(high level), the detection drive line L1P and the display drive line L2are similarly sequentially scanned in each embodiment, this is notlimitative. For example, the detection drive line L1P may be scanned bya plurality of drive electrodes, or randomly scanned.

Modification 3-2

For example, in each embodiment, the liquid crystal display device 442,which uses liquid crystal in a mode of TN (Twisted Nematic), VA(Vertical Alignment), ECB (Electrically Controlled Birefringence) or thelike, and the touch sensor 441 are integrated to configure the displaydevice with a touch detection function 44. However, a liquid crystaldisplay device using liquid crystal in a transverse electric field modesuch as FFS (Fringe Field Switching) mode or IPS (In-Plane Switching)mode and a touch sensor may be integrated with a touch sensor instead.For example, in the case of using liquid crystal in a transverseelectric field mode, a display device with a touch detection function44B may be configured as shown in FIG. 24. The figure shows an exampleof a relevant-part section structure of the display device with a touchdetection function 44B, showing a state where a liquid crystal layer 6Bis sandwiched between a pixel substrate 2B and a counter substrate 3B.Names or functions of other sections are the same as in the case of FIG.5, and therefore omitted to be described. In this example, unlike thecase of FIG. 5, a drive electrode 33 commonly used for display and fortouch detection is formed immediately above a TFT substrate 21, andconfigures part of the pixel substrate 2B. Pixel electrodes 22 aredisposed above the drive electrode 33 with an insulating layer 23 inbetween. In this case, all dielectrics including the liquid crystallayer 6B between the drive electrode 33 and a touch detection electrode34 contributes to formation of capacitance C1.

Modification 3-3

Furthermore, for example, while the liquid crystal display device 442and the touch sensor 441 are integrated in each embodiment, the deviceand the sensor may not be integrated. FIG. 25 shows a configurationexample of a capacitance-type touch panel 40C in the case that the firstembodiment is modified in such a way.

The capacitance-type touch panel 40C includes a Vcom generator 41, adrive control circuit 42C, a drive electrode driver 43, a touch sensor441, a multiplexer 47, a detection circuit 48, and a resistance R. Inthe modification, the drive control circuit 42C controls the driveelectrode driver 43 to generate only detection drive lines L1P and L1N.In addition, a drive signal Vcom is used only in the touch sensor 441,internal noise is not generated. Other operation is the same as in thefirst embodiment.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-154207 filedin the Japan Patent Office on Jun. 29, 2009, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalent thereof.

1.-14. (canceled)
 15. A capacitance-type touch panel comprising: aplurality of drive electrodes; a drive control circuit performingcontrol such that a drive signal for touch detection is selectivelyapplied to the drive electrodes; a plurality of touch detectionelectrodes arranged to form capacitance with the drive electrodes, andeach outputting a detection signal in synchronization with the drivesignal; and a detection circuit detecting an external proximity objectbased on the detection signal, wherein the drive control circuitcontrols application of the drive signal such that a positive drivesignal is selectively applied to predetermined regions of the display ina first period; a negative drive signal is applied to predeterminedregions of the display in a second period different from the firstperiod so that there is a difference in surface area of the driveelectrodes receiving the positive and negative drive signals for contactdetection thereby causing a time-average level of the detection signalboth in the first period and the second period to be shifted withrespect to a center voltage of the detection signal when a portion ofthe display is contacted or approached due to a difference incapacitance between the first period and the second period; and thedetection circuit detects the external proximity object based on a shiftof the time-average level of the detection signal both in the firstperiod and the second period with respect to the center voltage of thedetection signal.
 16. The capacitance-type touch panel according toclaim 15, wherein the drive signal is a signal having a periodicalwaveform including a period of a first voltage and a period of secondvoltage different from the first voltage, the drive control circuitselects a first group of drive electrodes and a second group of driveelectrodes from the plurality of drive electrodes in such a manner that,a total width of drive electrodes, belonging to the first group of driveelectrodes, within a base width corresponding to size of the externalproximity object is different from a total width of drive electrodes,belonging to the second group of drive electrodes, within the basewidth, at any position in a region where the drive electrodes arearranged, and then applies the first voltage and the second voltage ofthe drive signal to the selected drive electrodes of the first andsecond groups, respectively.
 17. The capacitance-type touch panelaccording to claim 16, wherein the drive control circuit selects thefirst group of drive electrodes in such a manner that the first group ofdrive electrodes configures a single strip region which shifts in amanner of time-divisional scanning.
 18. The capacitance-type touch panelaccording to claim 16, wherein the drive control circuit selects thesecond group of drive electrodes in such a manner that the second groupof drive electrodes are divided into a plurality of sub groupsdiscretely arranged.
 19. The capacitance-type touch panel according toclaim 15, wherein the drive control circuit selects the first group ofdrive electrodes and the second group of drive electrodes in such amanner that a total width of all drive electrodes belonging to the firstgroup is equal to a total width of all drive electrodes belonging to thesecond group.
 20. The capacitance-type touch panel according to claim15, wherein the drive signal is a signal having a periodical waveformincluding a period of a first voltage and a period of second voltagedifferent from the first voltage, and the drive control circuit selectsa group of drive electrodes configuring a single strip region from theplurality of drive electrodes, and controls application of the drivesignal in such a manner that the first voltage of the drive signal isapplied to the group of drive electrodes, and that a second voltage isnot applied to any drive electrode.
 21. The capacitance-type touch panelaccording to claim 15, wherein the detection circuit has an analogfilter performing high-band cutoff for cutting a band of frequenciesequal to or higher than a predetermined frequency.
 22. A displayapparatus with a touch detection function comprising: a plurality ofdrive electrodes; a drive control circuit performing control such that adrive signal for touch detection is selectively applied to the driveelectrodes; a plurality of touch detection electrodes arranged to formcapacitance with the drive electrodes, and each outputting a detectionsignal in synchronization with the drive signal; a detection circuitdetecting an external proximity object based on the detection signal;and a display section displaying an image based on an image signal,wherein the drive control circuit controls application of the drivesignal such that a positive drive signal is selectively applied topredetermined regions of the display in a first period; a negative drivesignal is applied to predetermined regions of the display in a secondperiod different from the first period so that there is a difference insurface area of the drive electrodes receiving the positive and negativedrive signals for contact detection thereby causing a time-average levelof the detection signal both in the first period and the second periodto be shifted with respect to a center voltage of the detection signalwhen a portion of the display is contacted or approached due to adifference in capacitance between the first period and the secondperiod; and the detection circuit detects the external proximity objectbased on a shift of the time-average level of the detection signal bothin the first period and the second period with respect to the centervoltage of the detection signal.
 23. The display apparatus with a touchdetection function according to claim 22, wherein the display section isconfigured with liquid crystal elements, and the drive signal for touchdetection also serves as part of a display drive signal for driving thedisplay.
 24. The display apparatus with a touch detection functionaccording to claim 23, wherein the display drive signal includes a pixelsignal based on the image signal and a common drive signal, the displaysection performs display operation by means of polarity-inversiondriving where a polarity of an application voltage which is defined bythe pixel signal and the common drive signal and is applied to each ofthe liquid crystal elements is time-divisionally inverted, and the drivesignal for touch detection also serves as the common drive signal. 25.The display apparatus with a touch detection function according to claim22, wherein a positive-negative asymmetric variation appearing in thedetection signal associated with drive of the display section iscompensated based on the image signal.
 26. The display apparatus with atouch detection function according to claim 22, wherein the drive signalis a signal having a periodical waveform including a period of a firstvoltage and a period of second voltage different from the first voltage,and the drive control circuit selects a group of drive electrodesconfiguring a strip region from the plurality of drive electrodes, andcontrols application of the drive signal such that the first voltage ofthe drive signal is applied to the group of drive electrodes, and asecond voltage is not applied to any drive electrode.
 27. The displayapparatus with a touch detection function according to claim 22, whereinthe detection circuit performs compensation for a variation due todisplay noise through eliminating a positive-negative asymmetric displaynoise component from the detection signal based on the image signal, thedisplay noise component appearing in the detection signal associatedwith drive of the display section.
 28. A method of driving a touchpanel, comprising steps of: selectively applying a drive signal fortouch detection to a plurality of drive electrodes; allowing each of aplurality of touch detection electrodes to output a detection signal insynchronization with the drive signal when an external proximity objectexists, the touch detection electrodes being arranged form capacitancewith the drive electrodes, and the detection signal being applied suchthat a positive drive signal is selectively applied to predeterminedregions of the display in a first period and a negative drive signal isapplied to predetermined regions of the display in a second perioddifferent from the first period so that there is a difference in surfacearea of the drive electrodes receiving the positive and negative drivesignals for contact detection thereby causing a time-average level ofthe detection signal both in the first period and the second period tobe shifted with respect to a center voltage of the detection signal whena portion of the display is contacted or approached due to a differencein capacitance between the first period and the second period; anddetecting the external proximity object based a shift of thetime-average level of the detection signal both in the first period andthe second period with respect to the center voltage of the detectionsignal.